This invention relates to physical quantity distribution sensors and it further relates to physical quantity distribution sensor driving methods.
Recently, there have been increasing demands for physical quantity distribution sensors used for the detection of the one-/two-dimensional distribution of various physical quantities. In the field of solid-state imaging technology for detecting a light intensity as a physical quantity, a so-called amplification type solid-state imaging device has attracted attention. A typical amplification type solid-state imaging device has a plurality of picture elements each comprising a photoelectric conversion section operable to generate a signal charge by photoelectric conversion of light incident thereon, a storage region for storing the signal charge, and a driving element such as a field-effect transistor (FET) for providing a signal according to the signal charge. The storage region is connected to a gating control region of the driving element such as a FET gate region and bipolar transistor base region, to achieve control of the output value of the driving element by the electrical potential of the storage region that varies according to signal charge amounts stored therein. Some amplification type solid-state imaging devices employ a storage region that serves also as a transistor gating control region.
Although such an imaging device has amplifying transistors functioning as driving elements allocated to each pixel, these amplifying transistors differ in transistor characteristic from one another. If the characteristic of a transistor in the absence of signal charge, for instance, the threshold voltage, Vt, of a FET, varies, this results in variations in the output value of the transistor even when each photoelectric conversion section is illuminated by the same amount of incident light thereby equalizing the electrical potentials of the gating control regions. As a result, spatially fixed noise, known as fixed pattern noise (FPN), occurs, therefore causing severe damage to the qualities of image.
Japanese Patent Application Laying Open Gazette No. 5-252445 shows an amplification type solid- state imaging device with a view to preventing the occurrence of FPN. This prior art imaging device is described with reference to FIG. 8. An amplifying transistor M1 for amplifying a sensor potential, VS, is disposed for each pixel. A feedback circuit 3 including a differential amplifier 2 is provided which supervises the channel electrical potential of the transistor M1 and fixes same at a reference electrical potential, VRxe2x80x2, at reset operation time. A reset is carried out by adjustment of VS using the output of the amplifier 2 at the time when a reset transistor M3 is electrically conductive. The FIG. 8 imaging device circuitally achieves a reduction of the variation in Vt of the transistor M1.
In such a prior art imaging device, at the time of supervising the channel electrical potential of the transistor M1 of each pixel, a switching transistor M2 is placed in an electrically non-conductive (off) state and an electrical potential at a node between the transistors M1 and M2 is applied to an input section of the amplifier 2. The reason for this may be that the imaging device employs a structure in which the magnitude of a current flowing in the transistor M1 is read as an output, IS, and it is impossible to detect the channel electrical potential of the transistor M1 at the time when the transistor M2 is electrically conductive. It is required that the electrical potential at the node between the transistors M1 and M2, V0, be applied to the amplifier 2. This requires extra interconnection lines for providing connections between each pixel and the amplifier 2. In order to perform feedback on every pixel by the single amplifier 2, it is necessary to newly provide transistors to each pixel in addition to the switching transistors used for pixel selection. Accordingly, it is impractical for area sensors, in which a great number of pixels are 2-D arranged, to adopt the above-described structure.
Feedback operations by the amplifier 2 are performed, not at the time when signal charge stored in a photo sensor 1 is read through the transistors M1 and M2, but at the time when the transistor M2 is in the non-conductive state. In accordance with the prior art technique, feedback is not carried out based on the output in the same state as that of the actual output operation time, which results in insufficient improvements on the accuracy of feedback.
Accordingly, an object of the present invention is to provide physical quantity distribution sensors and its driving methods for getting rid of noise due to variations in the characteristics of driving elements by high-accuracy feedback.
The present invention provides a physical quantity distribution sensor comprising a plurality of unit cells, each such unit cell including: an information storage region responsive to a physical stimulus and capable of a transition from a first electrical potential state to a second electrical potential state according to the physical stimulus; a driving element for providing at an output portion thereof an electrical potential according to the electrical potential state of the information storage region; and a switching element connected to the output portion of the driving element; the physical quantity distribution sensor further comprising: an output section for receiving, when the switching element is electrically conductive, an output from the driving element which is connected to the switching element and outputting a signal according to the electric potential state of the information storage region; an output adjustment section for receiving, when the switching element is electrically conductive, the output from the driving element and adjusting the first electrical potential state of the information storage region in order that the output from the driving element may substantially equal a reference electrical potential; and a unit cell selector for controlling an electrically conductive/non-conductive state of the switching element.
In a preferred embodiment, the driving element is a MOS transistor having: a gate connected to the information storage region; a source for functioning as the output portion and connected to the output section; and a drain for receiving a supply voltage.
In a preferred embodiment, the physical quantity distribution sensor further comprises a load element connected to the source of the driving element wherein the driving element and the load element together form a source follower circuit.
In a preferred embodiment, the switching element is a MOS transistor having: a gate for receiving a signal from the unit cell selector; a drain connected to the source of the driving element; and a source connected to the output section.
In a preferred embodiment, the information storage region has: a sensing section for converting the physical stimulus into an electric charge; and a storage section for storing the electric charge.
In a preferred embodiment, the sensing section is a p-n junction type photoelectric conversion element.
In a preferred embodiment, the storage section is a p-n junction type capacitor element.
In a preferred embodiment, each of the plurality of unit cells further includes a reset element operable to perform a forcible reset of the electrical potential state of the information storage region to the first electrical potential state in response to a reset pulse.
In a preferred embodiment, the reset element is a MOS transistor that receives at a gate region thereof the reset pulse.
In a preferred embodiment, the reset element is a MOS transistor that receives at a gate region thereof the output of the output adjustment section.
In a preferred embodiment, the output of the output adjustment section is supplied, through the reset element, to the information storage region at the time when the reset element performs a reset of the electrical potential state of the information storage region.
In a preferred embodiment, the output of the output adjustment section is supplied to a gate region of the reset element when the reset element performs a reset of the electrical potential state of the information storage region.
In a preferred embodiment, the plurality of unit cells being divided into a plurality of groups; the output adjustment section containing a plurality of functionally identical adjusters; and the plurality of groups being assigned the adjusters, respectively.
In a preferred embodiment, each such adjuster is formed by an operational amplifier, or an inverting differential amplifier, or a comparator.
In a preferred embodiment, the plurality of adjusters are fed the reference electrical potential through a common line.
In a preferred embodiment, the plurality of unit cells are arranged forming a matrix of rows and columns; the unit cell selector has row selection circuits for selecting respective rows of unit cells of the matrix; and an output of the row selection circuit causes the switching elements of a selected row of unit cells to conduct and allows the reset pulse to be transmitted to the reset elements of the selected row of unit cells.
In a preferred embodiment, (a) the plurality of unit cells are arranged forming a matrix of rows and columns; (b) the unit cell selector has: column selection circuits for selecting respective columns of unit cells of the matrix; and column selection elements connected between each of the columns of unit cells and the output section; and (c) the column select element supplies, in response to an output of the column selection circuit, the output of the driving element in the unit cell in a selected column to the output section.
In a preferred embodiment, (a) the plurality of unit cells are arranged to form a matrix of rows and columns; (b) the unit cell selector has: column selection circuits for selecting respective columns of unit cells of the matrix; column selection elements connected between each of the columns of unit cells and the output section; and selected column reset elements connected between each of the columns of unit cells and an input section at which the reset pulse is applied; (c) the column select element supplies, in response to an output of the column selection circuit, the output of the driving element in the unit cell in a selected column to the output section; and (d) the selected column reset element applies, in response to the output of the column selection circuit, the reset pulse to the reset element in the selected column.
The present invention provides a physical quantity distribution sensor comprising a plurality of unit cells each including: an information storage region responsive to a physical stimulus and capable of a transition from a first electrical potential state to a second electrical potential state according to the physical stimulus; a driving element for providing at an output portion thereof an electrical potential according to the electrical potential state of the information storage region; and a switching element connected to the output portion of the driving element; the physical quantity distribution sensor further comprising: an output section for receiving, when the switching element is electrically conductive, an output from the driving element which is connected to the switching element and outputting a signal according to the electric potential state of the information storage region; an output adjustment section for receiving the signal from the output section and adjusting the first electrical potential state of the information storage region in order that the signal may have an electrical potential level substantially equal to a reference electrical potential; and a unit cell selector for controlling an electrically conductive/non-conductive state of the switching element.
In a preferred embodiment, the driving element is a MOS transistor having: a gate connected to the information storage region; a source for functioning as the output portion and connected to the output section; and a drain for receiving a supply voltage.
In a preferred embodiment, the physical quantity distribution sensor further comprises a load element connected to the source of the driving element wherein the driving element and the load element together form a source follower circuit.
In a preferred embodiment, the switching element is a MOS transistor having: a gate for receiving a signal from the unit cell selector; a drain connected to the source of the driving element; and a source connected to the output section.
In a preferred embodiment, the information storage region has: a sensing section for converting the physical stimulus into an electric charge; and a storage section for storing the electric charge.
In a preferred embodiment, the sensing section is a p-n junction type photoelectric conversion element.
In a preferred embodiment, the storage section is a p-n junction type capacitor element.
In a preferred embodiment, each of the plurality of unit cells further includes a reset element operable to perform a forcible reset of the electrical potential state of the information storage region to the first electrical potential state in response to a reset pulse.
In a preferred embodiment, the reset element is a MOS transistor that receives at a gate region thereof the reset pulse.
In a preferred embodiment, the reset element is a MOS transistor that receives at a gate region thereof the output of the output adjustment section.
In a preferred embodiment, the output of the output adjustment section is supplied, through the reset element, to the information storage region at the time when the reset element performs a reset of the electrical potential state of the information storage region.
In a preferred embodiment, the output of the output adjustment section is supplied to a gate region of the reset element when the reset element performs a reset of the electrical potential state of the information storage region.
In a preferred embodiment, the output adjustment section containing a single adjuster; and each of the unit cells being assigned the single adjuster.
In a preferred embodiment, the plurality of unit cells are arranged forming a matrix of rows and columns; the unit cell selector has row selection circuits for selecting respective rows of unit cells of the matrix; and an output of the row selection circuit causes the switching elements of a selected row of unit cells to conduct and allows the reset pulse to be transmitted to the reset elements of the selected row of unit cells.
In a preferred embodiment, the physical quantity distribution sensor further comprises a sampling hold circuit connected to the output section.
In a preferred embodiment, (a) the plurality of unit cells are arranged to form a matrix of rows and columns; (b) the unit cell selector has: column selection circuits for selecting respective columns of unit cells of the matrix; column selection elements connected between each of the columns of unit cells and the output section; and selected column reset elements connected between each of the columns of unit cells and an input section at which the reset pulse is applied; (c) the column select element supplies, in response to an output of the column selection circuit, the output of the driving element in the unit cell in a selected column to the output section; and (d) the selected column reset element applies, in response to the output of the column selection circuit, the reset pulse to the reset element in the selected column.
In a preferred embodiment, the physical quantity distribution sensor further comprises feedback row selection elements connected between each of the columns of unit cells and the output adjustment section, wherein the feedback row selection element is operable to transmit the output of the output adjustment section to the reset element in the unit cell in the selected column.
The present invention provides a method of driving a physical quantity distribution sensor comprising a plurality of unit cells, each such unit cell including: an information storage region responsive to a physical stimulus and capable of a transition from a first electrical potential state to a second electrical potential state according to the physical stimulus; a driving element for providing at an output portion thereof an electrical potential according to the electrical potential state of the information storage region; and a switching element connected to the driving element; the driving method comprising the steps of: sending a signal according to the electric potential state of the information storage region by virtue of the driving element through the switching element, when the switching element is electrically conductive; and adjusting the first electrical potential state of the information storage region in order that the output of the driving element may substantially equal a reference electrical potential, when the switching element is electrically conductive.
The present invention provides a method of driving a physical quantity distribution sensor comprising a plurality of unit cells, each such unit cell including: an information storage region responsive to a physical stimulus and capable of a transition from a first electrical potential state to a second electrical potential state according to the physical stimulus; a driving element for providing at an output portion thereof an electrical potential according to the electrical potential state of the information storage region; and a switching element connected to the driving element; the driving method comprising the steps of: sending a signal according to the electric potential state of the information storage region by virtue of the driving element selected through the switching element, when the switching element is electrically conductive; and adjusting the first electrical potential state of the information storage region in order that the signal may have an electrical potential level substantially equal to a reference electrical potential, when the switching element is electrically conductive.
In a preferred embodiment, the adjustment step is carried out by a feedback circuit.
In a preferred embodiment, the adjustment step is carried out at the time of performing a reset of the electrical potential state of the information storage region to the first electrical potential state.
In a preferred embodiment, the plurality of unit cells are arranged forming a matrix of rows and columns; and the adjustment step is performed on every unit cell in the selected row after a step of sending a signal according to the electrical potential state of the information storage region for all unit cells in each row of the matrix is completed.
In a preferred embodiment, the plurality of unit cells are arranged forming a matrix of rows and columns; and after a step of sending a signal according to the electrical potential state of the information storage region for a single unit cell in a selected row of the matrix is completed, the adjustment step is performed on the unit cell.
In a preferred embodiment, during a step of sending signals according to the electrical potential state of the information storage region for each unit cell in the selected row, the signals are subjected to sampling.